The present invention relates generally to modular refrigeration systems and, more specifically, to refrigeration systems that use a cold producing unit for removing heat from a desired space and a eutectic-based thermal storage unit to boost the refrigeration capacity during peak loads.
Known refrigeration systems generally have used conventional vapor compression Rankine cycle devices as the cold producing unit for a given space. In a typical Rankine cycle apparatus, the refrigerant in the vapor phase is compressed in a compressor so as to cause an increase in temperature. The hot, high-pressure refrigerant is then circulated through a heat exchanger, called a condenser, where it is cooled by heat transfer to the surrounding environment. As a result, the refrigerant condenses from a gas back to a liquid. After leaving the condenser, the refrigerant passes through a throttling device where the pressure and the temperature are reduced. The cold refrigerant leaves the throttling device and enters a second heat exchanger, called an evaporator, located in or near the refrigerated space. Heat transfer with the evaporator and the refrigerated space causes the refrigerant to evaporate or to change from a saturated mixture of liquid and vapor into a superheated vapor. The vapor leaving the evaporator is then drawn back into the compressor so as to repeat the refrigeration cycle.
One alternative to the use of a Rankine cycle system is a Stirling cycle cooler. The Stirling cycle cooler is also a well-known heat transfer mechanism. Briefly described, a Stirling cycle cooler compresses and expands a gas (typically helium) to produce cooling. This gas shuttles back and forth through a regenerator bed to develop much greater temperature differentials than may be produced through the normal Rankine compression and expansion process. Specifically, a Stirling cooler may use a displacer to force the gas back and forth through the regenerator bed and a piston to compress and expand the gas. The regenerator bed may be a porous element with significant thermal inertia. During operation, the regenerator bed develops a temperature gradient. One end of the device thus becomes hot and the other end becomes cold. See David Bergeron, Heat Pump Technology Recommendation for a Terrestrial Battery-Free Solar Refrigerator, September 1998. Patents relating to Stirling coolers include U.S. Pat. Nos. 5,678,409; 5,647,217; 5,638,684; 5,596,875; and 4,922,722, all incorporated herein by reference.
Stirling cooler units are desirable because they are nonpolluting, efficient, and have very few moving parts. The use of Stirling coolers units has been proposed for conventional refrigerators. See U.S. Pat. No. 5,438,848, incorporated herein by reference. The integration of a free-piston Stirling cooler into a conventional refrigerated cabinet, however, requires different manufacturing, installation, and operational techniques than those used for conventional compressor systems. See D. M. Berchowitz et al., Test Results for Stirling Cycle Cooler Domestic Refrigerators, Second International Conference.
To date, the use of Stirling coolers is not known in refrigerators in general and in beverage vending machines, glass door merchandisers (xe2x80x9cGDM""sxe2x80x9d), and dispensers in particular. Therefore, a need exists for adapting Stirling cooler technology to conventional beverage vending machines, GDM""s, dispensers, and the like.
Regardless of the nature of the cold producing unit, another issue with modern refrigeration systems as a whole is the ability to provide cooling in an efficient manner even during peak loads. One means to provide additional cooling to the system as a whole during such peak load periods is through the use of a thermal storage unit. Although such thermal storage units in general are known in the art, the efficient use of such systems demands that the cold producing unit and the thermal storage unit be designed and balanced to address the particular use environment intended for refrigeration system.
As a result, a given refrigeration system may need, for example, a large capacity cold producing unit while only occasionally needing a thermal storage unit, i.e., the system may have a large average heat load but low peak demand loads. Likewise, both the cold producing unit and the thermal storage unit may need to be maximized for extended peak demand loads. Any number of different scenarios may apply.
Although a refrigeration system may need to address certain use parameters, changing the refrigeration capacity of a given system is often difficult. The particular components of the system generally may not be expandable or easily modified. Further, the components in the system may well be proprietary to a given manufacturer such that the components may not be interchangeable with those of another manufacturer or even with a refrigeration system of a different capacity. The ability to vary the capacity of a given system is therefore very limited.
What is needed, therefore, is a means by which the refrigeration capacity of a given refrigeration unit may be varied depending upon the intended use. The various components of the refrigeration unit therefore must be interchangeable and expandable. The cost of such elements, however, should be reasonable as compared to known components and units.
The present invention thus provides a refrigeration system for chilling an enclosure. The system may include a thermal transfer pathway with a cold producing unit and a thermal storage unit connected to the pathway via a number of quick disconnect fittings.
Specific embodiments of the invention may include using shut off devices as the quick disconnect fittings. The cold producing unit may include one or more modular devices. The cold producing unit also may be a Stirling cooler, a Rankine cycle device, or a Transcritical Carbon Dioxide cycle device. The thermal transfer pathway may include a secondary liquid refrigerant loop with a heat transfer liquid therein. The cold producing unit may be connected to the thermal transfer pathway via a heat exchanger. The heat exchanger may be a fluid or a solid heat exchanger. The thermal transfer pathway may include a pump. The thermal storage unit may include one or more modular devices. The thermal storage unit may include a eutectic material, such as a phase change material, therein. The thermal storage unit may include a heat exchanger positioned therein. The thermal storage unit also may include a temperature sensor.
The refrigeration system further may include an enclosure heat exchanger connected to the thermal transfer loop. The heat exchanger may be positioned for chilling the enclosure. A temperature sensor may be positioned about the heat exchanger so as to determine the temperature within the enclosure. The thermal transfer pathway may include a by-pass valve and a by-pass line so as to by-pass the heat exchanger if desired. The by-pass valve may shut the heat exchanger when the temperature within the enclosure is at or below a predetermined temperature and open the heat exchanger when the temperature is above the predetermined temperature. A control system may operate the thermal transfer pathway, the by-pass valve, and the cold producing unit.
The refrigeration system further may include a heat transfer block in communication with the enclosure heat exchanger. The heat transfer block may include a fluid line therein. The thermal storage unit also may include a fluid line and an agitator therein.
A further embodiment of the present invention may provide for a refrigeration system for chilling an enclosure. The system may include a fluid pathway with a heat transfer fluid therein. One or more Stirling coolers and one or more thermal storage units may be connected to the fluid pathway. A heat exchanger may be positioned in communication with the enclosure. The fluid pathway may include a by-pass valve such that the heat transfer fluid may or may not pass through the heat exchanger. The Stirling coolers and the thermal storage units may connect to the fluid pathway via a number of quick disconnect fittings. The thermal storage unit may include a eutectic material, such as a phase change material, therein.
The refrigeration system further may include a temperature sensor positioned within the enclosure such that the by-pass valve allows the heat transfer fluid to flow though the enclosure heat exchanger when the temperature within the enclosure exceeds a predetermined temperature as sensed by the temperature sensor. The system further may include a control system in communication with the by-pass valve and the temperature sensor.
A further embodiment of the present invention may provide for a beverage dispenser. The dispenser may include a heat transfer pathway with a heat transfer fluid therein. One or more modular cold producing units, one or more modular thermal storage units, and a heat exchanger may be connected to the heat transfer pathway. A product pathway may be positioned about the heat exchanger. The modular cold producing units may be Stirling cycle coolers. The modular thermal storage units may include a eutectic material therein. The modular cold producing units and the modular thermal storage units may be connected to the heat transfer pathway via a number of quick disconnect fittings. The heat transfer pathway may include means to modify the number of modular cold producing units connected thereto so as to modify the total cold producing capacity of the beverage dispenser. The heat transfer pathway also may include means to modify the number of modular thermal storage units connected thereto so as to modify the total thermal storage capacity of the beverage dispenser. The beverage dispenser further may include a heat transfer block in communication with the heat exchanger and the product pathway for heat transfer therethrough.
A further embodiment of the present invention may provide for a refrigeration system for chilling an enclosure. The system may include a thermal transfer pathway with a number of modular cold producing units and modular thermal storage units connected thereto. The number of modular cold producing units and the number of modular thermal storage units connected to the thermal transfer pathway may be modified so as to modify the capacity of the refrigeration system as a whole. A heat exchanger also may be connected to the heat transfer pathway so as to chill the enclosure.
A method of the present invention may provide for determining the configuration of a refrigeration system. The method may include the steps of determining an expected average heat load for the refrigeration system, installing one or more modular cold producing units with a capacity sufficient to accommodate the expected average heat load, determining an expected peak demand load for the refrigeration system, and installing one or more modular thermal storage units with a capacity sufficient to accommodate the expected peak demand load. The modular cold producing units may be Stirling cooler units and the modular thermal storage units may include a eutectic material.
The method further may include the steps of operating the refrigeration system, determining an average heat load for the refrigeration system, and modifying the number of the modular cold producing units to accommodate the average heat load. The step of modifying the number of the modular cold producing units may include adding or removing one or more of the units. The method further may include the steps of operating the refrigeration system, determining a peak demand load for the refrigeration system, and modifying the number of the modular thermal storage units to accommodate the peak demand load. The step of modifying the number of the modular thermal storage units may include adding or removing one or more of the units.
The method further may include the steps of revising the expected average heat -load for the refrigeration system and modifying the number of the modular cold producing units to accommodate the expected average heat load. The method further may include the steps of modifying the expected peak demand load for the refrigeration system and modifying the number of the modular thermal storage units to accommodate the expected peak demand load.